This invention relates to electronic grid line continuity test devices and more particularly to an improved handheld Hall Effect Sensor sweep probe instrument designed for testing window grid heaters or the like. The invention has specific applications in testing automotive rear window electric defoggers having a series of parallel grid lines deposited on the inside surface of the glass. Heretofore electrical continuity testing of the grid lines required an inspector to work from within the vehicle and touch each individual grid line with a voltmeter lead with the other lead grounded. This time consumming procedure allows only random spot-check inspection of the heater grids during the vehicle production line assembly.
The present invention has as an object to provide a continuity test device for window glass electrical grids that does not require any direct electrical connection with the grid lines.
It is another object to provide electrical continuity inspection of interior surface vehicle window grid heaters by testing each bank of grid lines exterior of the vehicle with a hand-held pen-like module or probe by sweeping the probe over the window outer surface. A further object is to provide a grid line test probe that will detect low level grid line voltages by minimizing the instruments sensitivity to stray electronic waves prevalent in industrial sites.
The novel probe of the invention may, in a repair mode, be moved across individual grid lines to check for continuity. Indicating means are provided in the form of light emitting diodes, an audio alert signal or the like incorporated within the probe. The probe in another mode is initially passed over the outside glass surface in a single transverse sweep across a bank of grid lines to provide a go or no-go production line check. Current, supplied to the grid lines from the vehicle's battery source flows in each parallel grid line, thus generating separate localized magnetic fields or regions having a predetermined flux density.
A pair of side-by-side Hall Effect Sensors, positioned near a glide face of the probe, are spaced a predetermined distance less than the transverse spacing of the grid lines. The sensor active portions are directed toward the opposed outside surface of the glass. As the probe is moved across the glass outer surface transverse to the direction of the grid lines each sensor is alternately exposed to a maximum flux intensity region and a minimum flux intensity region created by the energized grid lines. The sensors are spaced relative to the grid lines such that when one sensor is exposed to a maximum flux density region the other sensor is exposed to a minimum flux density region. The offset output voltages of the sensors, in the form of out-of-phase sinusoidal wave forms, are fed to a pair of input pins of an instrumentation amplifier which amplifies the difference between the input voltages. The output of the instrumentation amplifier is a composit pulsed waveform signal. A low pass filter circuit removes any direct current component of the signal.
The probe circuit further amplifies and compares the signal with a reference voltage. When a pulse of significant magnitude is sensed by the circuit it triggers on an electronic valve which turns-on visual and/or acoustical signal means indicating to the operator each function grid line.
It is therefore a feature of the present invention to provide a handheld Hall Effect backlite pen instruement to readily detect breaks in vehicle window electric heater grid lines without requiring in-car inspection. These and other objects and features of the invention will appear from consideration of the preferred embodiments made with reference to the accompanying drawings.